Guard Cells in leaves

Tony Travis ajt at
Tue Dec 3 05:24:00 EST 1996

Tammer Riad wrote:
> Could someone please explain the function of guard cells in leaves, how
> they are activated (opening) and deactivated (closing), and the different
> theories surrounding them?

Hello, Tammer.

Guard cells 'guard' the stomatal aperture, and control most of the gas
exchange between the leaf and the surrounding air because the leaves are
usually covered with a wax cuticle that is virtually impermeable.

Guard cells are unusual in plants in that they are capable of quite
rapid movements to open and close the stomatal aperture in response to
internal and external stimuli. The leaf movements of Mimosa pudica are
another example of rapid turgor-mediated movements in plants.

The 'stomatal apparatus' consists of a pair of guard cells around the
pore or 'stoma' which are often surrounded by specialised subsidiary
cells. The arrangement of these cells is characteristic of particular
species and is used to identify the origin of leaf litter, or even the
remains of plant material in animal faeces.

The stomatal mechanism remains one of the most interesting, and
controversial subjects investigated by botanists. Current thinking is
that guard cell turgor is the result of an active H+ ion-transport
mechanism in the cell membrane controlled by direct responses of the
guard cells to stimuli such as light and CO2 level, mediated by calcium
signalling mechanisms in the rest of the plant.

There is a huge literature on the subject and if you are iterested in
further reading have a look at a textbook like Salisbury, F.B and Ross
C.W. (1991), Plant Physiology, California:Wadsworth Inc. Chapter 4. "The
Photosynthesis-Transpiration Compromise" which gives a good explanation.

A more detailed technical account can be found in: Willmer, C.M. and
Fricker, M.D. (1995) Stomata. 2nd Edition Chapman and Hall, London.

Dr. A.J.Travis,                     |  mailto:ajt at
Rowett Research Institute,          |
Greenburn Road, Bucksburn,          |   phone:+44 (0)1224 712751
Aberdeen AB2 9SB, Scotland, UK.     |     fax:+44 (0)1224 716687

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